ZSM-5 Coatings on β-SiC Monoliths:  Possible New Structured Catalyst for the Methanol-to-Olefins Process

Abstract

Structured zeolite/silicon carbide composites were succesfully synthesized by ZSM-5 coatings deposited on macroscopic β-SiC foams with medium surface area. A homogeneous coverage of the support (30 wt % zeolite) by ZSM-5 crystals, having 1 µm average size, was reached after a double-coating procedure. The ZSM-5/β-SiC composite materials were characterized by BET, XRD, SEM, and H/D exchange methods. 27 Al MAS NMR analysis revealed that all aluminum was present in a tetrahedral coordination, thus sitting in the zeolite framework. The existence of a nanoscopic layer of silica and silicon oxycarbide on the surface of the support ensures the strong anchoring of the zeolite crystals on the β-SiC substrate. The lack of secondary chemical reaction between the synthesis solution and the support allows a precise control of the Si/Al ratio in the final zeolite. The use of ZSM-5 coated β-SiC foam packings in the methanol-to-olefins reaction presents substantial activity/selectivity improvements compared to conventional zeolite packings. Moreover, the structured composites exhibit a higher stability toward deactivation by coking, compared to the powdered form of the zeolite.

Zeolitic Materials with Hierarchical Porous Structures

“…Both effects result in the observed higher selectivity and improved stability towards deactivation of the catalyst. Similar trends of catalyst stability towards deactivation were reported by Ivanova et al, [ 102 ] who investigated the MTO reaction over MFI in situ coated ß-SiC foams and MFI powder.…”

“…Furthermore, applying zeolite crystals on structured supports by ex situ coating techniques yields a layer consisting of randomly oriented zeolite crystals which is typically characterized by a certain voidage, thus allowing for intercrystalline diffusion. [102][103][104] In Tables 4 and 5 typical examples for both the ex situ and the in situ techniques are summarized.…”

Phosphorous Modified ZSM-5 Zeolites: Impact on Methanol Conversion into Olefins

“…ZSM-5 zeolite catalysts are often used and different strategies aiming to improve selectivity toward light olefins have been tempted: change in operating conditions, reactor configuration, tailoring Brønsted acidity, and structured catalyst development [14].…”

Efficient Synthesis of Dimethyl Ether over HZSM‐5 Supported on Medium‐Surface‐Area β‐SiC Foam

“…[15,16] The high-resolution transmission electron microscopy (TEM) image of the SiC surface ( Figure 2) shows the presence of a thin (2-3 nm), uniform layer of an amorphous mixed phase of SiO 2 and SiO x C y .…”